In a manufacturing process of a semiconductor device, a target object to be processed such as a semiconductor wafer or the like is repeatedly subjected to various kinds of processing such as a film forming, an etching, a heat treatment and a modification treatment. For example, there is known a CVD (Chemical Vapor Deposition) method to form a thin film on a surface of a semiconductor wafer. In the CVD method, a semiconductor wafer is arranged within a processing chamber of a processing apparatus. A processing gas containing a source gas is introduced into the processing chamber to generate a reaction product. A thin film made of the reaction product is deposited on the surface of the semiconductor wafer.
In recent years, there is also known an ALD (Atomic Layer Deposition) method as a film forming method. In the ALD method, a source gas and a reaction gas are alternately supplied into a processing chamber to form thin films one layer after another each of which has a thickness of atomic level or molecular level. The ALD method can provide a film having a good quality and can accurately control the film thickness. For that reason, the ALD method draws attention as a manufacturing method of a semiconductor device which is becoming more scaled down.
In case where a thin film of, e.g., TiN, is formed by the ALD method, the thin film is deposited by repeatedly performing a series of the following steps i) through iv) for example.
i) A source gas, e.g., a TiCl4 gas, is supplied into a processing chamber, thereby causing TiCl4 to adhere onto a wafer surface.
ii) The inside of the processing chamber is purged by a N2 gas to remove the remaining source gas from the processing chamber.
iii) A reaction gas, e.g., an NH3 gas, is supplied into the processing chamber to react with the TiCl4 adhered onto the wafer surface to thereby form a thin layer of TiN film.
iv) The inside of the processing chamber is purged by a N2 gas to remove the remaining gas from the processing chamber.
In the ALD method, as described in the TiN film formation example above, supplies and cutoffs of different kinds of gases including the source gas need to be intermittently and repeatedly performed within a short period of time. In an ALD apparatus, the supply and cutoff of the gas is performed with an electromagnetic valve, which is provided in a gas supply path through which the gas is supplied to the processing chamber, and is opened and closed by a signal transmitted from a control unit based on a gas supply recipe.
In case of the film forming process performed by the ALD method, as compared with the film forming process performed by the CVD method, the time required in opening and closing the valve once becomes shorter and the opening/closing frequency of the valve becomes extremely high. For that reason, troubles such as failure of the valve and degradation of the valve components can be more frequently made in the ALD method than in the CVD method. In order to satisfactorily perform the film forming process in the ALD method, the changeover of different kinds of gases is required to be precisely controlled. If the opening and closing of the valve is not accurately performed as instructed by the control unit, the possibility of forming a poor film will be increased.
In the ALD apparatus, it is therefore imperative to prevent any occurrence of an abnormality in the valve beforehand. Since the opening and closing speed of the valve is very fast in the ALD apparatus, there is a problem in that a conventional control system has a difficulty in monitoring the opening and closing of the valve on a real time basis to check the operation status of the valve.
In respect of the film forming process performed by the ALD method, Japanese Patent Application Publication No. 2002-329674 (e.g., FIG. 1) (corresponding to U.S. Patent Application Publication No. 2002/0127745A1) describes a valve control system including a programmable logic controller configured in communications with a system control computer and operatively connected to an electrically-controlled valves. In this valve control system, the valve control refresh time is reduced to 10 milliseconds or less.
Japanese Patent Application Publication No. 2010-153420 (e.g., the claims) describes an ALD apparatus including a control device for controlling the opening and closing states of valves and a pattern preparing device for preparing a valve changeover pattern for setting the opening and closing states of the valves. In the ALD apparatus described in JP2010-153420A, the pattern preparing device writes the prepared valve changeover pattern in an internal area of the control device and stores the prepared valve changeover pattern in a storage medium of the pattern preparing device. The control device performs the changeover of the valves based on the valve changeover pattern written in the internal area thereof, writes the opening and closing states of the valves at that time in the internal area thereof and stores the opening and closing states of the valves written in the internal area thereof in the storage medium of the pattern preparing device. With the ALD apparatus described in JP2010-153420A, ex-post monitoring on a valve operation error can be performed.
Japanese Patent Application Publication No. 2003-286575 (e.g., the claims) (corresponding to U.S. Patent Application Publication No. 2003/0143747A1) describes a method in which a monitoring is performed by detecting characteristic parameters such as a pressure in a gas flow path and a valve vibration, and providing a signal indicative of the characteristic parameters as a function of time by a sensor in order to measure changes in gas pulses supplied into a processing chamber in an ALD apparatus.
While JP2002-329674A and JP2010-153420A disclose the ALD apparatuses capable of coping with the high-speed opening and closing of the valves, no consideration is given to how to observe an abnormality of a valve on a real time basis. Further, in JP2003-286575A, a trouble of a valve is indirectly monitored based on the change in the characteristic parameters. Thus, it may be time-consuming to detect the trouble of the valve because the opening and closing of the valve is not directly monitored.
Further, in addition to the hardwarely occurred trouble described above, an error in a software may occur easily in the ALD apparatus coping with the high-speed opening and closing of the valves. For example, in a control unit for controlling the ALD apparatus, a multi-task process in which multiple tasks are carried out at the same time by a plurality of software is performed. In this case, if a task priority in the multi-task process is improperly set, the opening/closing timing in a control signal for opening and closing the chamber valve 37 at a high speed may not correspond to the opening/closing timing set by the recipe, so that the opening/closing operation of the valves is delayed in the actual operation, which makes it difficult to realize a highly reliable ALD process.